Reliable markers for malignant tumor differentiation are necessary for accurate diagnosis of cancer. In addition, many of these markers may prove useful as targets for therapy, especially if they are required for growth or metastasis of cancer cells. Present therapies for cancer include surgery, radiation and chemotherapy. For the most part, chemotherapy involves the use of general DNA synthesis inhibitors, DNA structure disruptors and DNA adducts in which chemical agents are added to the primary DNA molecule. The problem with these approaches is that they are not specific to cancer cells, so there are many serious negative side effects associated with chemotherapy such as nausea, hair loss, gastrointestinal disorders and disruption of normal brain function.
The Wnt-signaling pathway has been known for some time to be abnormally activated in colon cancer. Pygopus is a downstream effector of this pathway. The problem we faced was to determine how to use human Pygopus in cancer diagnostic and therapy.
The canonical Wnt/β-catenin pathway is normally required for embryonic development and for the controlled proliferation of adult stem cells. The critical mediator of the pathway is β-catenin, a multifunctional protein whose activity depends on its cytoplasmic localization. In the absence of Wnt signaling, the majority of β-catenin is associated with the plasma membrane, where it is required with E-cadherin for cell adhesion. Cytoplasmic levels of free β-catenin are regulated by a destruction complex consisting of tumor suppressor proteins that include Glycogen Synthase Kinase-3 beta (GSK-3β), Axin, Adenomatous Polyposis Coli (APC) and Casein Kinase I which cooperatively direct cytoplasmic β-catenin for proteosome-mediated degradation. The binding of Wnt to its receptor relieves degradation of cytosolic β-catenin, allowing it to accumulate in the nucleus where it assembles into a complex that binds to genes involved in cell cycle progression. This complex is composed of Leukemia Enhancer/T-cell Factor (LEF)/TCF-1, B-cell lymphoma-9 protein (BCL-9) and the nuclear protein, Pygopus. Localized chromatin remodeling effects by Pygopus, specifically bound to BCL-9 are thought to allow access of the basal transcriptional machinery to initiate target gene transcription.